This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goals of this project are to obtain crystal structural determinations for rhodopsin and its complexes with other proteins. Rhodopsin is the G-protein coupled receptor (GPCR) that serves as a photoreceptor molecule in the retina. Absorption of a photon causes a structural change in the protein that initiates a signal transduction signal via its G-protein (transducin) that is processed by the vision system. Understanding the nature of the activation and signaling process requires molecular structural information for the activated receptor and its complexes. This information will be important for understanding the molecular basis for vision, but also for understanding the more general process of activation of GPCRs. GPCRs are a major family of membrane receptors that serve as drug targets for a large fraction of the commercially important pharmaceuticals. Just as our initial structure determination of rhodopsin affected the investigation and modeling of other GPCRs, the structure of activated rhodopsin and/or its complex with transducin will provide a basis for further development of therapeutic agents for this class of proteins.